Purging water with reactant air pump powered by operational fuel cell system during shutdown

ABSTRACT

The air blower ( 18 ) of a fuel cell power plant ( 9 ) is used to force water out of the coolant flow fields ( 27 ) of a fuel cell stack ( 10 ), a coolant pump ( 35 ) and a heat exchanger ( 40 ) through a valve ( 46 ) which is closed during normal operation. The water removal occurs as part of a shutdown procedure in which the fuel cell stack continues to operate so that it provides the power for the air pump and to assist in water removal (such as retaining low vapor pressure). The water flow to an accumulator ( 33 ) is blocked by a valve ( 29 ) during the shutdown procedure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/996,512 filed Nov. 24, 2004.

TECHNICAL FIELD

This invention relates to using the reactant air pump of a fuel cellpower plant to force water out of coolant fields, coolant passagewaysand coolant equipment, as part of a shutdown procedure, utilizing powergenerated by the fuel cell power plant while it is still operational,just prior to shutdown.

BACKGROUND ART

Damage can occur to fuel cell power plant components as a result ofwater freezing, whenever a fuel cell power plant is to benon-operational in an ambient environment in subfreezing temperatures.It is known to have an accumulator placed at the lowest point in thecoolant system so that freezable coolant that actually flows through thefuel cell stack can drain toward the accumulator. It is also known touse external pumps to blow air or inert gas through various parts of thesystem in order to purge water therefrom.

However, use of an external pump increases the cost, size, weight andcomplexity of a fuel cell power plant and may be prohibitive in fuelcell power plants used to power electric vehicles. In addition, when thefuel cell power plant is shut down, an auxiliary power source, such asbatteries or supercapacitors, must be utilized in order to power thepurging pump equipment. This either reduces auxiliary power availablefor various functions, such as melting of ice or warming of the fuelcell stack, or else requires larger, heavier and more expensiveauxiliary power sources, which also may be prohibitive in electricvehicles.

DISCLOSURE OF INVENTION

Objects of the invention include: purging water from coolant channels,passages and equipment without the use of either an auxiliary purge pumpor auxiliary power; purging coolant water from a fuel cell power plantwithout requiring additional expense, weight or space for auxiliarypumping equipment or auxiliary power; and improved purging of water froma fuel cell power plant in anticipation of subfreezing temperatures.

According to the present invention, the reactant air pump of a fuel cellpower plant is utilized to purge water from water coolant flow fields,coolant passages and coolant equipment, utilizing fuel cell power plantpower while the fuel cell power plant is still operational, duringshutdown of the fuel cell power plant in anticipation of beingnon-operational at subfreezing temperatures.

In accordance with the invention, coolant water is blown out of thecoolant flow fields, coolant pump, and a coolant heat exchanger by theair pump using power generated by the fuel cell power plant.

The invention is disclosed in a simple embodiment but is equallyapplicable to coolant systems operating with different pumparrangements, including arrangements having a primary pump and asecondary pump utilized to educt froth from an air separator.

Other objects, features and advantages of the present invention willbecome more apparent in the light of the following detailed descriptionof exemplary embodiments thereof, as illustrated in the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE is a simplified, schematized, block diagram of a fuelcell power plant employing the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

Referring to the FIGURE, a fuel cell power plant 9 employing theinvention includes a fuel cell stack 10 which may be a conventionalpolymer electrolyte proton exchange membrane (PEM) fuel cell stack,including conventional anode flow fields 11, the configuration andnature of which are not peculiar to the present invention and need notbe described further.

The stack 10 includes cathode flow fields 13 which provide oxidant gasto the cathode catalyst. The cathode flow fields are provided air at aninlet 16 through a conduit 17 from an air pump 18, receiving air througha conduit 19 from ambient. The exit 20 of the cathode flow fields isexhausted through a conduit 21 and a valve 22 to ambient 23.

The stack 10 has coolant flow fields 27, the exit 28 of which isconnected through a valve 29 and conduits 30, 31 to the inlet 32 of aconventional accumulator 33. From the accumulator, coolant flows througha conduit 34, a coolant pump 35, over a conduit 38 and through theprimary flow passage 39 of a heat exchanger 40, and thence through aconduit 41 into the inlet 42 of the coolant flow fields 27. The heatexchanger 40 is conventional, the details of it are not important to theinvention and it is not described further. The accumulator may have anoutlet 43 through a valve 44.

In accordance with the invention, air from the conduit 17 is applied,during shutdown, through a conduit 45, a valve 46 and a conduit 47 tothe coolant flow field exit 28. During normal operation, the valve 46 isclosed, the valve 29 is open, and the pump 35 is operational.

During shutdown, the pump 35 is off, the valve 29 is closed and thevalve 46 is open. However, the fuel cell power plant 9 is stillproducing electricity, at least of sufficient magnitude so as to providefull power to the air pump 18. This is a first aspect of the presentinvention. The fuel cell power plant operation may be regulated duringshutdown, such as by means of a controller and an auxiliary load.

Maintaining the operation of the fuel cell power plant 9 without coolantflow may cause the temperature of the stack 10 to increase above thenormal operating temperature, to about 65° C.-80° C., for instance. Thetemperature rise results in an increase in vapor pressure of the waterremaining in the coolant flow channels as the air passes through thecoolant flow fields, thereby assisting in dryout of the coolant flowfields. This shutdown process may last for between a fraction of aminute and several minutes, depending on the system configuration andsize of the conduits and channels.

During shutdown, the primary flow of air is over the conduit 45 throughthe now-open valve 46, over the conduit 47 and backwardly through theexit 28 of the coolant flow fields 27. From the inlet 42 of the coolantflow fields, water which is blown ahead of the air, and moisture whichis picked up by the air, will flow over the conduit 41, through the heatexchanger 40, and over the conduit 38, backwardly through the coolantpump 35 and over the conduit 34 into the accumulator 33.

The air pump 18 may be a positive displacement pump, or any othersuitable pump which can provide sufficient pressure and flow volume toclear water from the coolant flow fields 27, the heat exchanger 40, andthe coolant pump 35, while at the same time providing sufficient processair to the cathode flow fields for generating the required pump power.

The invention may be used to clear water from less than all of the waterpassages in a fuel cell power plant, if desired.

Thus, although the invention has been shown and described with respectto exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the invention.

1. A fuel cell power plant comprising: a plurality of fuel cellsarranged in a stack including coolant flow fields, said fuel cellsincluding oxidant reactant gas flow fields; an air pump that provides,during normal operation, air to said oxidant reactant gas flow fields;and means operable as part of a procedure of shutting down the operationof said stack of fuel cells, while said stack of fuel cells is stillproducing electrical power, for connecting said air pump to waterpassages comprising at least one of (a) the coolant flow fields in saidfuel cell stack, (b) a coolant pump that during normal operation causescoolant to flow through said coolant flow fields, and (c) the primaryflow passage of a coolant heat exchanger interconnected with saidcoolant flow fields, said air pump utilizing at least a portion of saidelectrical power to operate during said shutdown procedure.
 2. A fuelcell power plant comprising: a plurality of fuel cells arranged in astack including coolant flow fields, said fuel cells including oxidantreactant gas flow fields; an air pump that provides, during normaloperation, oxidant reactant gas to said oxidant reactant gas flowfields, and, as part of a procedure of shutting down the operation ofsaid stack of fuel cells, while said stack of fuel cells is stillproducing electrical power, is powered by at least a portion of saidelectrical power; a coolant pump that during normal operation causescoolant to flow through said coolant flow fields; a heat exchangerhaving a primary flow passage interconnected with said coolant pump andsaid coolant flow fields; and means operable during said procedure forconnecting said air pump to water passages comprising at least one of(a) said coolant flow fields, (b) said coolant pump, and (c) said heatexchanger.
 3. A method of operating a fuel cell power plant having aplurality of fuel cells arranged in a stack including coolant flowfields, said fuel cells including oxidant reactant gas flow fields whichare provided air by an air pump during normal operation, a coolant pumpthat during normal operation causes coolant to flow through said coolantflow fields, and a heat exchanger having a primary flow passageinterconnected with said coolant pump and said coolant flow fields, saidmethod comprising: as part of a procedure of shutting down the operationof said stack of fuel cells, while said stack of fuel cells is stillproducing electrical power, connecting said air pump to water passagescomprising at least one of (a) said coolant flow fields, (b) saidcoolant pump, and (c) said heat exchanger, and using at least a portionof said electrical power to operate said air pump.